An internal combustion engine system includes a canister to suction vaporized fuel generated in a fuel tank. The vaporized fuel suctioned to the canister is left from the canister by an intake negative pressure developing in an intake passage during an operation of the internal combustion engine and is supplied to the internal combustion engine together with the intake air for combustion treatment (hereinafter this process is referred to as a purge process).
When the vaporized fuel left from the canister is suctioned to the internal combustion engine, an air-fuel ratio is enriched by the amount. In view of this, for example, to reduce deterioration of emission, an amount of fuel injection needs to be corrected so as to be reduced according to the amount of supplied vaporized fuel in the purge process (hereinafter also referred to as an amount of purge).
When the fuel is injected divided into multiple times in one combustion cycle, so-called multiple-stage injection, performing the amount reduction correction possibly makes an injection pulse width in one time smaller than a pulse width at the minimum (hereinafter also referred to as a minimum pulse width) at which stable fuel injection is possible. In consideration of this point, JP4491387B discloses restricting the amount of purge such that all injection pulse widths in the multiple-stage injection do not fall below the minimum pulse width.